The present invention relates to a monitor system for a multiplex equipment, or more in particular to a monitor system suitably used for self-diagnosis.
In conventional monitor systems for multiplex equipments, as disclosed in JP-A-No. 56-49508 or the "INOUT CHECK SYSTEM OF MULTIPLE EQUIPMENT" presented at the 1979 The Institute of Electronics and Communication Engineers of Japan, input and output signals of a multiplex equipment are bridged to a monitor circuit in the form of bipolar signal, a switching circuit of which is used to select an input-output signal for comparison out of the bridged signals, and the signals thus selected are converted into a unipolar signal form.
The above-mentioned prior art systems have the disadvantage in that the packaging and economical considerations for the switching circuit for selecting an input-output signal for comparison are omitted, thereby posing the problem of insufficient size reduction and economization.
As a matter of fact, in the case where the switching circuit is configured of a mechanical switch such as a relay, the switching operations are performed at the rate of as many as several tens to several hundreds of msecs, thus leading to the problem of a shortened service life. Realization of a satisfactory mechanical switch requires a high-cost relay. If an electronic switch is constructed of diodes or transistors to make a switching circuit, on the other hand, switching of a high-frequency bipolar signal would require flat frequency characteristics and small crosstalks over a wide band, which would make it difficult to configure and package a switch circuit and necessitate high-cost parts. Further, in view of the fact that an input-output signal is bridged to a comparator circuit in the form of bipolar signal, the disadvantage results that low-bit-rate and high-bit-rate input interfaces are required for the comparator circuit.